Neanderthal mothering The debate on how long to breastfeed now has a Neanderthal spin with analysis of a fossilised tooth suggesting primitive mothers breastfed exclusively for just seven months.

The claim is based on an analysis of barium concentration in different layers of tooth enamel, which also reveals the Neanderthal child was completely weaned at 1.2 years.

The finding by Australian and US researchers, published today in Nature, comes out of research aimed at more accurate pinpointing of the moment of birth in the tooth enamel record.

Barium levels in teeth have in other research been shown to be higher during breastfeeding in human children, dropping during weaning, and then again after the conversion to solid food.

The mineralisation of barium in human tooth enamel already starts in the second trimester of pregnancy, when the immature teeth are still in the jawbone.

"Barium is higher in breast milk compared with prenatal exposure because the placenta is restricting movement of the barium across to the foetus," says lead author Dr Christine Austin, a post-doctoral fellow at the University of Sydney's dental faculty.

These fluctuations in barium levels are recorded in the structure of tooth enamel - almost like growth rings on a tree.

Comparing humans and monkeys

Researchers initially used naturally shed teeth from human children and captive macaque monkeys in whom breastfeeding habits were carefully documented, then applied the technique to the ancient molar of a young Neanderthal.

This analysis showed the Neanderthal child was exclusively breastfed for at least seven months, then breastfeeding was supplemented for another seven months.

"After this point, barium levels in enamel returned to baseline prenatal levels, indicating an abrupt cessation of breastfeeding at 1.2 years of age," the researchers write.

"People are trying to find out the life history of our ancestors or hominid species - they want to look at when species replaced other species or when they diverged and one way of defining species is development," she says.

Humans differ from other primates in that we wean relatively early despite having long childhoods.

"If we can work out that Neanderthals had a much earlier weaning time or a longer childhood compared to another hominid species then we can say that's when they diverged and this is where humans have gotten this type of development from," she adds.

Extracting a mystery

It also has implications around the mystery of why Neanderthals disappeared about 30,000 years ago, while Homo sapiens thrived.

One theory suggests they weaned later than H. sapiens - shorter breastfeeding would have meant quicker intervals between children and more rapid population expansion for humans.

"Our approach will allow the evaluation of hypotheses that Neanderthal young routinely weaned at later ages than Upper Palaeolithic hominims, or possessed faster life histories than modern humans," they write.

Study co-author Dr Manish Arora, at the Institute of Dental Research at Westmead Millennium Institute, stresses the tests were done with only one Neanderthal sample and "it would be reckless of us to say this would be the norm for all Neanderthals".

"We look forward to this technique being applied to more Neanderthal samples so that a more reliable consensus on weaning patterns in Neanderthals may be made," he says.

The researchers are also using the technique to examine the change in absorption of metals such as lead and manganese from foetus to newborn.

"We think that the prenatal period might be a period of susceptibility for children so we look at the elements and compare prenatal to post-natal exposure, and now we've got that elemental biomarker of birth, we can be pretty sure we're looking at the prenatal part of the tooth," Austin says.

The technique might also be applied to gain a more accurate measure of the benefits of breastfeeding.

"One application is that we know that breastfeeding can be linked to health outcomes with children so if we can take these teeth and see precisely how long breastfeeding went for, we can more accurately link that to the health outcomes and find out how much breastfeeding might reduce that risk," says Austin.